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Groups > comp.lang.java.programmer > #31831

Re: Getting results of command execution

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On 06/19/2015 10:50 AM, FredK wrote:
> On Thursday, June 18, 2015 at 2:40:15 PM UTC-7, Jeff Higgins wrote:
>> On 06/18/2015 10:30 AM, FredK wrote:
>>> On Wednesday, June 17, 2015 at 6:28:51 PM UTC-7, Jeff Higgins wrote:
>>>> On 06/17/2015 05:57 PM, FredK wrote:
>>>>> On Wednesday, June 17, 2015 at 2:14:45 PM UTC-7, Eric Sosman wrote:
>>>>>> On 6/17/2015 4:56 PM, FredK wrote:
>>>>>>> I want to execute a set of commands and get the results. So I start with,
>>>>>>> on Unix;
>>>>>>>       process P = Runtime.getRuntime().exec("commandA; commandB");
>>>>>>>
>>>>>>> or on Windows
>>>>>>>       process P = Runtime.getRuntime().exec("commandA & commandB");
>>>>>>>
>>>>>>> How do I get the results of the output AND error output in the order they are created?
>>>>>>>
>>>>>>> If I use this type of coding:
>>>>>>> [...]
>>>>>>> I get all of the stdout, followed by all of the stderr. But suppose commandA writes some output, then some errors, then more outputs, etc. I want to retrieve them in that order.
>>>>>>
>>>>>>         You could try using a ProcessBuilder to set up your Process, and
>>>>>> use its redirectErrorStream() method to merge stdout and stderr before
>>>>>> calling start().  But even then, you'll be at the mercy of whatever
>>>>>> buffering takes place in the external process itself: If that process
>>>>>> holds on to stdout data until it's got a bufferload, but emits stderr
>>>>>> data right away (this is the default behavior for many C programs),
>>>>>> the mingled data will be temporally scrambled no matter what you do
>>>>>> on the receiving side.
>>>>>>
>>>>>>
>>>>> I'm not sure I can accomplish what I want;
>>>>
>>>> I'm sure that you're clear on what you want to accomplish
>>>> but so far you haven't made it clear to me. It sounds as if
>>>> you want to plant a Java process between a user and his CLI
>>>> (sh, cmd.exe, ...) or perhaps replace it?
>>>>
>>>> <http://labs.neohapsis.com/2008/04/17/connect-back-shell-literally/>
>>>>
>>>>> I haven't been able to find anything that will let me execute multiple commands in the same invocation.
>>>>>
>>>>> I want to pass along user commands to be executed, and there might be a "cd" imbedded in the string, or setting some environment variables, or any of a multitude of things that cause one command to depend on the results of some previous command(s), so it I can't just execute each command in a separate process.
>>>>>
>>>
>>> The requirement is essentially that I want to include a panel in my program that acts like a shell. So throughout the lifetime of the program, in addition to interacting with the program the user can also use it as if it were a shell - kind of like a Unix xterm, with additional capabilities. For example, the user could type "ls", then point to a file name, right-click on it and it would open up an editor for that file (based on what kind of file it is), or if it is the name of a directory, cd to that directory and possibly execute ls in that directory. Typing "<Ctrl>+U" would execute "cd ..;pwd;ls", plus other features.
>>>
>>> I have written something like this in C using Motif, and it works fine - I just fork at the beginning and the child becomes a shell, and I redirect the pipes such that I have access to the shell's input, output, and error streams.
>>>
>>> But I don't know how to do this in Java.
>>>
>>
>> Thanks for the explanation.
>> That is pretty much what I had imagined you are looking for.
>> I'm afraid such a thing is well beyond my skill set and
>> I'm impressed that you've got something working albeit in
>> another programming environment.
>> I wish you good luck and would love to here back about
>> your successes.
>
> Here's what I am now doing:
> First, I store the current working directory as currentDir.
> Then I create a meta-command from the actual command:
>
>     private final String[]     cbufWindows    = { "cmd", "/c", "" };
>     private final String[]     cbufLinux      = { "bash", "-c", "" };
>     String[] buf;
>     String command;
>        if ( platform == Platform.UNIX ) {
>           command = "cd " + dir + "; " + cmd + "; echo " + END_STR
>                 + "; echo $?; pwd";
>           cbufLinux[2] = command;
>           buf = cbufLinux;
>        } else if ( platform == Platform.WINDOWS ) {
>           command = "pushd " + dir + " & " + cmd + " & echo " + END_STR
>                 + " & cd &popd";
>           cbufWindows[2] = command;
>           buf = cbufWindows;
>        } else {
>           return; // unimplemented for other platforms
>        }
>
>        Runtime rt = Runtime.getRuntime();
>        Process p = rt.exec(buf);
>
> Here, Platform is an enum defined by me, and END_STR is a sentinel that is just a constant long string of gibberish unlikely to be input by the user or output by a command; this is to determine when the command actually ends.
>
> Note that in my meta-command I first cd to the current directory, execute the command, echo the ENDSTR, then echo the (possibly new) current directory.
>
> When reading the output of the command, I look for the sentinel, then read the echoed directory and store it back in "currentDir".
>
> This works fine as long as the command does not require interactive user input, but is sufficient for my needs.
>
I'm kinda tempted to ask why but probably shouldn't.
<http://www.linusakesson.net/programming/tty/>
Well, what the heck. Why?

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Thread

Getting results of command execution FredK <fred.l.kleinschmidt@gmail.com> - 2015-06-17 13:56 -0700
  Re: Getting results of command execution Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-06-17 17:14 -0400
    Re: Getting results of command execution FredK <fred.l.kleinschmidt@gmail.com> - 2015-06-17 14:57 -0700
      Re: Getting results of command execution Martin Gregorie <martin@address-in-sig.invalid> - 2015-06-17 23:07 +0000
      Re: Getting results of command execution Jeff Higgins <jeff@invalid.invalid> - 2015-06-17 21:26 -0400
        Re: Getting results of command execution FredK <fred.l.kleinschmidt@gmail.com> - 2015-06-18 07:18 -0700
        Re: Getting results of command execution FredK <fred.l.kleinschmidt@gmail.com> - 2015-06-18 07:30 -0700
          Re: Getting results of command execution Jeff Higgins <jeff@invalid.invalid> - 2015-06-18 17:37 -0400
            Re: Getting results of command execution FredK <fred.l.kleinschmidt@gmail.com> - 2015-06-19 07:50 -0700
              Re: Getting results of command execution Jeff Higgins <jeff@invalid.invalid> - 2015-06-19 21:33 -0400
                Re: Getting results of command execution Jeff Higgins <jeff@invalid.invalid> - 2015-06-19 21:56 -0400
                Re: Getting results of command execution Jeff Higgins <jeff@invalid.invalid> - 2015-06-19 23:02 -0400
                Re: Getting results of command execution Jeff Higgins <jeff@invalid.invalid> - 2015-06-20 11:11 -0400
                Re: Getting results of command execution Jeff Higgins <jeff@invalid.invalid> - 2015-06-20 12:14 -0400
                Re: Getting results of command execution Jeff Higgins <jeff@invalid.invalid> - 2015-06-20 20:58 -0400
          Re: Getting results of command execution Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-06-19 11:01 -0400
      Re: Getting results of command execution Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-06-18 08:38 -0400
  Re: Getting results of command execution Jeff Higgins <jeff@invalid.invalid> - 2015-07-03 23:41 -0400

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